1. Field of the Invention
The present invention relates to improvements in a pressurized type gasification apparatus which includes a gasification furnace main body having a water-cooled wall structure and a duct having a water-cooled wall structure and containing therein a group of gas cooling heat-exchangers for recovering heat from gas produced in the gasification furnace main body.
2. Description of the Prior Art
Every one of FIGS. 4 to 6 illustrates a different example of a pressurized type coal gasification apparatus in the prior art.
At first, FIG. 4 shows one example of such apparatus having a single-wall structure, in which reference character a designates a gasification furnace main body, character b designates a water-cooled wall, character c designates a heat insulating material, character d designates a pressure vessel, and character e designates an ash hopper. In a pressurized type gasification apparatus, since the interior of the gasification furnace main body is at high-temperature and high-pressure, in the case of a furnace wall having a single-wall structure such as the illustrated example, in view of a structural strength it was necessary to form the furnace wall as an extremely thick wall structure. However, not only is a thick furnace wall costly to manufacture but there is also a shortcoming in that the furnace is quickly damaged because a thermal radiation effect cannot be obtained. Thus, this water-cooled structure does not adapt well to the high-temperature and high-pressure conditions of the interior of the furnace and is not economical if a sufficient wall strength is to be provided.
Hence, as shown in FIG. 5, a pressurized type gasification apparatus having a so-called double-wall structure, in which a gasification furnace main body is disposed within a pressure vessel, was proposed (Japanese Patent Application No. 60-48202 (1985), Laid-Open Japanese patent Specification No. 61-207492 (1986)). This double-wall structure is constructed of a gasification furnace main body 01 and a pressure vessel 06 containing the former therein. The inner pressure of the pressure vessel 06 is maintained at a pressure equal to or a little lower than the inner pressure of the gasification furnace main body 01. A pressure difference arises due to the high pressure within the gasification furnace main body 01 being present in a stepped portion of the gasification furnace main body 01. In this case, the wall of the gasification furnace main body 01 can be thin. Also, a high thermal radiation effect can be produced by employing, for example, a water-cooled wall structure. Therefore, there is an advantage in that the gasification furnace main body has a long life.
However, in the case of employing such a double-wall structure, the pressure within the pressure vessel 06 must be maintained at a certain fixed pressure in correspondence with the pressure within the gasification furnace main body 01. Therefore, in the example shown in FIG. 5, a pressurized inert gas 040 is injected to the interior of the pressure vessel 06 (the exterior of the gasification furnace main body 01). In this case, the pressure of the inert gas fed into the pressure vessel 06 must be varied in correspondence with the pressure change within the gasification furnace main body 01 produced upon operation of the apparatus. Consequently, there is a shortcoming in that a complicated device or equipment is necessary for adjusting and controlling the feeding pressure of the inert gas by detecting the pressure within the furnace by means of a differential pressure gauge 041.
In order to eliminate these shortcomings, a pressurized type gasification apparatus illustrated in FIG. 6 was proposed (Japanese Patent Application No. 60-221324 (1985), Laid-Open Japanese Patent Specification NO. 62-81489 (1987)). In this apparatus, an interior of a pressure vessel 06 accommodating a gasification furnace main body 01 and an interior of a pressure vessel 013 accommodating a water-cooled wall 014 surrounding a heat-exchanger group 07 communicating with the interior of the gasification furnace main body 01 communicate with each other through a balance pipe 016. And, at a slag ejection port 03 of the gasification furnace main body 01 is provided a gas sealing device 018 providing a water seal. In addition, at an outlet of the water-cooled wall 014 is provided a gas receiver 011 mounted to the pressure vessel 013, and between the water-cooled wall 014 and the pressure vessel 013, and between the water-cooled wall 014 and the pressure vessel 013 is formed a gas passageway 036 through which a produced gas at a low temperature can freely flow in and flow out.
In the apparatus shown in FIG. 6, the pressure within the pressure vessel 013 can be controlled in a self-balancing manner by allowing a low-temperature produced gas at the outlet of the water-cooled wall 014 surrounding the heat-exchanger group 07 to freely flow into the pressure vessel 013, and hence a constant pressure difference can be maintained conforming to the pressure variations within the gasification furnace main body 01. Consequently, pressure control can be achieved very economically and reliably without necessitating special pressure detector means or control means. In addition, by providing the outlet of the water-cooled wall 014 as a free end, a difference in thermal expansion between the water-cooled wall 014 and the pressure vessel 013 can be accommodated for. Furthermore, since the sealing device 018 employing a water seal is provided at the slag ejection port 03 of the gasification furnace main body 01, a difference in thermal expansion between the gasification furnace main body 01 and the pressure vessel 06 also can be accommodated for.
However, the pressurized type gasification apparatus shown in FIG. 6 and described is not considered to be favorable in view of performance for the following reasons, and especially for reasons of safety, because a low-temperature gas at the outlet of the water-cooled wall can freely flow into and flow out from the pressure vessel 013 without being subjected to any restriction.
That is, the gas flowing into the pressure vessel 013 fills the interior of the same vessel. And the gas coming into contact with the water-cooled wall 014 is partly heated by heat dissipating from the inside of the water-cooled wall resulting in a reduction of its specific gravity, whereby it rises along the water-cooled wall 014. A gas filling the upper portion is displaced downward due to a difference in the specific gravity of the gases. In other words, natural convection would occur within the pressure vessel 013. Since this low-temperature gas having fallen due to natural convection passes through the gas passageway 036, mixes into a principal flow and lowers the temperature of the produced gas, the condition of the gas fed to an apparatus in the succeeding stage becomes unstable. As this is caused by a natural convection phenomenon, it is difficult to preliminarily estimate the amount of temperature change, and it is impossible to control it.
In addition, when the produced gas at the outlet of the water-cooled wall 014 flows into the pressure vessel 013 as described above, an unburnt carbon content (char) contained in the produced gas also enters the pressure vessel. Char accumulating within the pressure vessel is undesirable in view of maintenance and management of the apparatus and from the viewpoint of safety because the accumulated material may ignite and may cause fire due to various circumstances and it may even create a disaster such as an explosion or the like.